1. Field of the Invention
The invention relates generally to control apparatus for controlling the operation of vending machines, and particularly to such control apparatus having improved product delivery motor home detection circuitry, speed control circuitry and power supply circuitry.
2. Description of the Prior Art
The overall operation of microprocessor controlled vending machines is generally well known to men of ordinary skill in the art. See, for example, U.S. Pat. Nos. 4,593,361, 4,498,570, 4,481,590, 4,372,464 4,354,613, 4,328,539, 4,233,660, 4,231,105 and 4,225,056. Consequently, such Operation is discussed in this application only to the extent it directly relates to the understanding of the present invention. Much of the art pertaining to vending machine product delivery motor home detection is described in U.S. Pat. No. 4,458,187 which is assigned to the assignee of the present invention and which is incorporated by reference herein. U.S. Pat. No. 4,458,187 describes a vending machine control and diagnostic apparatus for a vending apparatus having product delivery means such as an electrically operated actuator. An impedance element and a switch are connected in series with each other and in a parallel circuit with the actuator. Opening and closing of the switch are controlled by the operation of the actuator. Whether the actuator is in the appropriate position, open circuited or short circuited, is determined by the control and diagnostic apparatus' detection of changes in impedance of the parallel circuit. In several embodiments disclosed in U.S. Pat. No. 4,458,187, separate run and test signals are supplied to the actuator. In a further embodiment, a 24V DC run signal and a 5V RMS AC test signal are combined on a single wire. The test circuit in that embodiment includes a DC test circuit and an AC test circuit.
Additional prior art in the art of home detection is seen in control apparatus manufactured by Coin Acceptors, Inc. In particular, Coin Acceptors, Inc. employs a scheme which places a motor actuated single pole double throw switch in series with each motor. Home position is detected by detecting short switch openings occurring when the cam actuated switch very briefly opens and then closes at the home position. This scheme shorts the normal open and normal closed contacts of the switch. Only during switch transitions is a circuit "open" detected. This "open" is monitored and used to determine the home position. The system is fundamentally noise sensitive in that noise being received anywhere within the home detect circuitry may give a false home indication. Also, as the actual signal is non-repetitive, there is no way to "check again" the fact of the home position. Additionally, as motor current is passed through the switch contacts and is in fact switched by these contacts, switch life will be shortened.
U.S. Pat. No. 4,231,105 describes an encoding scheme for generating a series of pulses indicative of the speed of rotation of a motor in a vending machine and processing means responsive to the number of pulses during a predetermined period to remove motor power at appropriate times. This type of encoding scheme is generally well known for monitoring motor speed and position, however, it is unnecessarily complex and costly for certain vending machine applications.
Turning to the area of vending machine product delivery motor speed control, the prior art utilizes a regulated DC supply source to produce a carefully regulated and substantially constant DC supply of power in order to maintain constant speed of such motors. These schemes usually fall into two categories. In a first, series voltage regulators are used, and in a second, switch mode regulators connected to a filter which produces a relatively constant voltage output are used. The speed of the motors is usually not directly regulated, but with the normally constant load of a working DC motor, the use of a power supply which provides a relatively constant DC output voltage is sufficient to maintain relatively constant speeds of motor operation. The disadvantages of the use of such systems are the power dissipated in the series voltage regulators and the high cost of the switch mode power supply.
Almost all electronic circuits require a direct current (DC) source of power. Such a source of power is required for the electronic control systems typically found in modern vending machines because the components used, such as a microprocessor require 5V DC plus or minus 5%. Consequently, these systems include regulated supplies because the output voltage of unregulated supplies varies with load, changes in line voltage, and changes in temperature.